This emulates the "scrolling text" effect that is present in briefings.
It is not exactly the same since it just goes pixel wise and not by
character but it looks good enough.
This adds access to the command briefing data parsed from the mission
file to the scripting API so it can be used by the UI scripts for the
high res UI.
Also switches the animation support to using the generic anim to use
streaming to improve performance.
the-maddin